If this were me I would use my M-Audio Quattro and record 4 separate tracks that could be used to playback on 4 channel output. I would ask for 4 powered speakers like the QSC k8 or k10 allowing each output from 4 track recording going to each speaker in location desired. With the sub running a crossover 100 and below you should be able to keep one or two side by side and not feel like you can find the location of the sub. You may be able to find thinner speakers with the power and sound. I use audacity to run my sound in and out of the quattro and providing my 4 channel sound. You may find other DAW softwares that will work with your needs. M-audio Delta 1010, Delta 66, Windows XP.
With the mixer you can bring the 4 outputs down to single output and provide to Assistive Listening.
With the QSC powered speakers I could use wireless mic receivers connected to the mic input and amplified and connect the line guitar cable to the transmitters to the output side of the Quattro and deliver these four channels via 4 wireless links using the bodypacks on seperate signals. Leaving only the power cable to the wall at the speaker.
